The present invention relates generally to audio sound systems and more particularly concerns audio sound systems which can decode from two-channel stereo into multi-channel sound, commonly referred to as "surround" sound.
Typical prior art surround systems have utilized a variable matrix for decoding a given signal into multi-channel outputs. Such a system is disclosed in U.S. Pat. No. 4,799,260, assigned to Dolby Laboratories, as well as in U.S. Pat. No. 5,172,415 to Fosgate. Each of these patents discloses a variable output matrix which provides the final outputs for the system. Other designs, such as that shown in U.S. Pat. No. 4,589,129 to David Blackmet, disclose a system which does not include a variable output matrix but instead includes individual steering blocks for left, center, right and surround.
The inventions described in my U.S. Pat. Nos. 5,319,713 and No. 5,333,201 are major improvements over what has become commercially known and available as Dolby Surround.TM. and Dolby Pro Logic.TM., primarily in that those patents describe a means for providing directional information to the rear channels, a feature which the Dolby systems do not provide. This feature is very desirable in exclusive audio applications, as well as in applications where audio is synched to video (A/V), and is fully described in the above-cited patents.
The evolution of the surround sound system has seen the developers of such systems progressively attempt to develop the technology which would allow audio engineers the ability to place specific sounds at any desired location in the 360.degree. soundfield surrounding the listener. A recent result of this can be seen with the development of Dolby Laboratories' AC3 system, which provides five discreet channels of audio. However, there are at least two major drawbacks to such a system: (1) it is not backward-compatible with all existing material, and, (2) it requires digital data storage--not allowing for analog recording of data (i.e. audio tape, video tape, etc.). A Dolby AC3-encoded digital soundtrack cannot be played back through a Dolby Pro Logic system. It is desirable, therefore, to matrix an encoded recording down to a two-channel stereo recording and then have the ability to place specific sounds at any one of 6 or more predetermined locations as an individual, independent sound source when decoded. A six channel implementation of such a system might provide left front, right front, center, left rear, right rear and overhead locations. There are numerous other embodiments of the invention with many other possible channel configurations, as will be apparent to those skilled in the art.
In light of the prior art, it is a primary object of the present invention to provide a system which would decode a stereo signal into as many stand-alone, independent channels as desired. It is also an object of the present invention to provide a system which is compatible with all existing stereo material. It is another object of the present invention to provide a system which is compatible with material encoded for use with other existing suround systems. It is a further object of the present invention to provide a system that employs specifically encoded material which can be played back through any other existing decoding systems without producing undesirable results.